U.S. Pat. No. 2,993,025, granted July 18, 1961 to Alsup et al; U.S. Pat. No. 3,027,352, granted Mar. 27, 1962 to Walling et al; U.S. Pat. No. 3,459,789, granted Aug. 5, 1969 to Muller et al; U.S. Pat. No. 3,743,614, granted July 3, 1973 to Wolters et al; U.S. Pat. No. 3,787,353, granted Jan. 22, 1974 to Ishii et al; U.S. Pat. No. 3,960,984, granted June 1, 1976 to Kohan; U.S. Pat. No. 4,098,843, granted July 4, 1978 to Johnson; Japanese Patent Publication No. 22669/68, published Sept. 30, 1968; and Japanese Patent Publication No. 48051/75, published in 1975; all disclose various polyacetal compositions, both those based on homopolymers and those based on copolymers, and various techniques for stabilizing such compositions. Alsup discloses stabilization of polyacetal compositions by blending therewith a synthetic polyamide. Walling discloses that the thermal stability of certain polyacetal copolymer compositions is improved as compared with corresponding homopolymer. Muller discloses the use of certain monomeric urethane methylol ethers containing free hydroxyl groups as stabilizers for polyacetals. Wolters discloses stabilization of polyacetal compositions by blending therewith a combination of an alkaline earth metal compound and a monomeric ester of an (alkyl-hydroxylphenyl)-carboxylic acid with a polyol. Ishii discloses stabilization of polyacetal compositions by blending therewith a compound of the formula R(NHCOCH.sub.2 X).sub.n where R is a hydrocarbon group, X is a cyano or carbamoyl group, and n is 2-6. Kohan discloses stabilization of polyacetal compositions by blending therewith an amide oligomer. Johnson discloses stabilization of polyacetal compositions by blending therewith a dispersion of polyamide in a carrier resin. Japanese No. 22669 discloses stabilization of polyacetal compositions with ethylene-vinyl acetate copolymer and Japanese No. 48051 discloses stabilization of polyacetal compositions with epichlorohydrin polymers and metal soap, epoxy compounds or organic phosphites.
While each of the references discussed above disclose various means for improving the stability of polyacetal compositions, none disclose the stabilization system used in the compositions of the present invention.
U.S. Pat. No. 3,310,608, granted Mar. 21, 1967 to Matsubayashi et al. discloses polyacetal honopolymer compositions which have been modified to improve dyeability and transparency by melt blending therewith, among other things, vinyl alcohol polymers. None of the Examples use purified hydroxy containing polymer or oligomer and none of the Examples use hydroxy containing polymer or oligomer in the amounts used in the present invention.
U.S. Pat. No. 3,322,740, granted May 30, 1967 to Kiff et al. discloses acetal resins, which are not "polyacetals" as that term is used in describing the present invention, which resins are modified to improve impact strength by incorporation into such resins of an alkylene oxide-polyol polyether, in amounts of from about 10 to about 50 percent.
U.S. Pat. Nos. 3,406,129 and 3,406,130, granted Oct. 15, 1968 to Price and Neff, respectively, disclose melt blends of cellulose polymer having free hydroxyl groups with up to 50% of acetal polymer and colloidal dispersions of such blends with certain solvents for the cellulose polymer, which compositions are alleged to have improved melt strength and elongation.
U.S. Pat. No. 4,555,357, granted Nov. 26, 1985 to Kausga et al. discloses polyacetal resin compositions containing 0.1-15 weight percent of an amide of the formula ##STR1## where R is carboxylic acid residue, x and y are 0-10 and n is 1-6. None of the Examples disclose compounds of the above formula which are polymeric or oligomeric.
East German Patent No. 61,345, published Apr. 4, 1968, discloses polyacetal compositions modified with 1-15 weight percent of trimethylol propane as a plasticizer to impart increased resistance to breakage by bending.
None of the references discussed immediately above deal with stabilization of polyacetal compositions, and while some disclose incorporating hydroxy-containing polymers into polyacetal compositions, none disclose the particular hydroxy containing polymers used in the compositions of the present invention, or the unexpected improved stability resulting therefrom.